The present invention relates to a resin-encapsulated semiconductor device called xe2x80x9cQFNxe2x80x9d (Quad Flat Non-leaded package), and a method for manufacturing the same. More particularly, the present invention relates to a resin-encapsulated semiconductor device and a method for manufacturing the same in which a lead frame is machined so as to reduce the thickness of the device and to improve the reliability thereof.
In recent years, in order to reduce the size of portable electronic devices, there is a demand for high-density mounting of semiconductor components such as resin-encapsulated semiconductor devices. Along with this trend, semiconductor packages have been reduced in size and thickness. QFN type package is known in the art as one type of resin-encapsulated semiconductor device that can meet such a demand. In a QFN type package, an outer lead, which is otherwise protruding sideways from the package, is eliminated, with external electrodes for electrical connection to the mother board being provided on the bottom surface.
A conventional QFN type resin-encapsulated semiconductor device and a method for manufacturing the same will now be described.
FIG. 6A and FIG. 6B are a cross-sectional view and a bottom view, respectively, illustrating a structure of the conventional resin-encapsulated semiconductor device, wherein FIG. 6A is a cross-sectional view taken along line VIa-VIxe2x80x2a-VIa in FIG. 6B.
As illustrated in FIG. 6A and FIG. 6B, the conventional resin-encapsulated semiconductor device includes a die pad 102, a semiconductor chip 101 mounted on the die pad 102 and having an electrode pad on the upper surface thereof, a plurality of leads 103 for passing electric signals to the semiconductor chip 101, thin metal wires 104 made of, for example, Au (gold) for connecting the semiconductor chip 101 and leads 103 with each other, suspension leads 108 connected to the die pad 102, and an encapsulation resin 105 for encapsulating therein the semiconductor chip 101, the thin metal wires 104 and the die pad 102. Note that the bottom surface of the conventional resin-encapsulated semiconductor device illustrated herein is in a rectangular or square shape, and the leads 103 provided along the four sides of the bottom surface are exposed on the bottom surface and the side surface of the semiconductor device. Moreover, at each corner of the bottom surface, the suspension lead 108 is exposed. The die pad 102, the lead 103 and the suspension lead 108 are made of a metal containing Cu (copper), and the thickness thereof is substantially in the range of 200 xcexcm to 300 xcexcm. Moreover, the thickness of the semiconductor device including the encapsulation resin is about 800 xcexcm (0.8 mm) when the thickness of the semiconductor chip 101 is 200 xcexcm.
As described above, the conventional resin-encapsulated semiconductor device is a lead-less type resin-encapsulated semiconductor device, in which the leads 103 exposed on the bottom surface are used as external electrodes.
Moreover, the upper surface of the die pad 102 is located higher than the upper surface of the lead 103, as illustrated in FIG. 6A, whereby the semiconductor chip 101 can overlap with the lead 103 as viewed from above, thus increasing the chip area proportion in the resin-encapsulated semiconductor device. Therefore, the conventional resin-encapsulated semiconductor device is reduced in size and thickness as compared with a QFP (Quad Flat Package) in which the leads are protruding outwards.
Next, a method for manufacturing the conventional resin-encapsulated semiconductor device will be described.
FIG. 7A to FIG. 7D are cross-sectional views illustrating a process of manufacturing the conventional resin-encapsulated semiconductor device, taken along line VIa-VII in FIG. 6B.
First, in the step shown in FIG. 7A, a lead-frame-forming metal plate made of a copper (Cu)-based material and having a thickness of 200 to 300 xcexcm is prepared, and the metal plate is stamped or etched so as to form a lead frame including the die pad 102, semi-finished leads 103a, the suspension leads 108 for supporting the die pad 102 at their tips, and an outer frame (not shown) to which the ends of the semi-finished leads 103a and the suspension leads 108 are connected.
Then, the lead frame is pressed so as to bend the suspension leads 108 upwards, thereby upsetting the upper surface of the die pad 102 to be located higher than the upper surface of the semi-finished lead 103a. Since the pressing process requires a xe2x80x9cgrip marginxe2x80x9d, the raised portion of the suspension lead 108 is necessarily provided inside the outer frame.
Then, in the step shown in FIG. 7B, the semiconductor chip 101 is mounted on, and adhered to, the upper surface of the die pad 102 by using an adhesive such as a silver paste.
Then, in the step shown in FIG. 7C, the electrode pad of the semiconductor chip 101 mounted on the die pad 102 is electrically connected to the upper surface of the semi-finished lead 103a by using the thin metal wire 104 such as a gold wire.
Then, in the step shown in FIG. 7D, the mounted semiconductor chip 101, the die pad 102 and the thin metal wires 104 are encapsulated together with the encapsulation resin 105. In this process, the lower surface (opposing the upper surface) of the semi-finished lead 103a is left exposed.
Then, a portion of each semi-finished lead 103a connected to the outer frame of the lead frame that is protruding out of the encapsulation resin 105 is cut off, thereby forming the leads 103. Thus, the resin-encapsulated semiconductor device of a QFN type is obtained, in which the cut surface of each lead 103 is exposed on, and flush with, the side surface of the encapsulation resin 105.
When the upper surface region of the lead frame is encapsulated with the encapsulation resin 105, a sheet seal method is used, in which the resin encapsulation process is performed with a seal sheet being closely attached to the lower surface of the lead frame, thereby preventing the encapsulation resin from creeping onto the reverse surface of the lead frame. With this method, it is ensured that the lower surface of each lead is left exposed, thus realizing a one-side-encapsulated structure.
Note that in an actual manufacturing process, a plurality of resin-encapsulated semiconductor devices are formed on the same surface of a single lead frame.
In this way, the conventional resin-encapsulated semiconductor device, which are small and thin, is manufactured.
However, in the conventional resin-encapsulated semiconductor device, the upper surface of the die pad 102 is located higher than the upper surface of the lead 103, and thus the thickness of the upset is added, whereby it is difficult to further reduce the thickness thereof.
Moreover, in the conventional resin-encapsulated semiconductor device, the die pad 102 is located higher than the leads 103 by bending the suspension leads 108, whereby a bending stress is applied during the bending process to the suspension leads 108 and the die pad 102 contained in the encapsulation resin 105. Furthermore, a stress is also applied during the injection and curing of the encapsulation resin 105. Thus, the stress applied to the suspension leads 108 and the die pad 102 remains unremoved even after the resin encapsulation process, whereby the operating lifetime of the conventional resin-encapsulated semiconductor device may possibly be shortened under certain operating environments.
An object of the present invention is to provide a resin-encapsulated semiconductor device and a method for manufacturing the same, in which the thickness is further reduced and the stress applied to lead members in an encapsulation resin is reduced, thereby realizing a high reliability.
A resin-encapsulated semiconductor device of the present invention includes: a die pad provided by thinning a lower portion of a lead frame; a semiconductor chip mounted on the die pad; a plurality of leads provided by thinning an upper portion of the lead frame; a connection member for connecting the semiconductor chip and the lead with each other; a plurality of suspension leads connected to the die pad; and an encapsulation resin for encapsulating therein the die pad, the semiconductor chip, the leads, the connection member and the suspension leads, with a bottom surface and an outer side surface of each lead being exposed as an external terminal, wherein: an upper surface of the die pad is located higher than an upper surface of the lead; and a lower surface of the die pad is located higher than a lower surface of the lead.
With such a structure, the die pad and the lead are thinned while the upper surface of the die pad is located higher than the upper surface of the lead, whereby it is possible to reduce the thickness of the device while maintaining a high semiconductor chip area proportion, as compared with a conventional resin-encapsulated semiconductor device. Moreover, when the die pad and the lead are thinned to appropriate thicknesses, the stress occurring due to the resin encapsulation can be absorbed by the self flexural deformation of the die pad and the lead, thereby improving the reliability of the device.
In one embodiment of the present invention: the semiconductor chip is mounted with its principal surface facing up; and the connection member is a thin metal wire. In such a case, the resin-encapsulated semiconductor device is of a QFN type.
In one embodiment of the present invention: the semiconductor chip is mounted with its principal surface facing down; and the connection member is a bump made of a metal. In such a case, the size of the chip to be mounted can be increased as compared with a case where the connection member is a thin metal wire.
In one embodiment of the present invention, at least a portion of the semiconductor chip overlaps with the lead as viewed from above, whereby the size of the semiconductor chip to be mounted can be further increased. Thus, the semiconductor chip area proportion in the package is increased, whereby the size of the resin-encapsulated semiconductor device can be further reduced.
In one embodiment of the present invention, at least a portion of each of the die pad and the lead has a thickness of 100 xcexcm to 150 xcexcm, whereby the stress occurring due to the resin encapsulation can be effectively absorbed by the self flexural deformation of the die pad and the lead. Therefore, it is possible to improve the reliability of the device and to prolong the product lifetime. Moreover, the die pad and the lead are thinner than those in the prior art, whereby it is possible to reduce the thickness of the resin-encapsulated semiconductor device as a whole. Specifically, the thickness of the device can be reduced by 0.1 mm or more as compared with a conventional resin-encapsulated semiconductor device in which the thicknesses of the die pad and the lead are 200 to 300 xcexcm.
A method of the present invention is a method for manufacturing a resin-encapsulated semiconductor device including a die pad, a semiconductor chip mounted on the die pad, a lead connected to the semiconductor chip by a connection member, and a suspension lead, the method including the steps of: (a) preparing a lead frame including the die pad, the lead and the suspension lead for supporting the die pad; and (b) thinning a lower portion of the die pad and an upper portion of the lead so that an upper surface of the die pad is located higher than an upper surface of the lead, and a lower surface of the die pad is located higher than a lower surface of the lead.
With this method, the upper surface of the die pad can be located higher than the upper surface of the lead through the step (b) of thinning the die pad and the lead. Therefore, as compared with a case where the die pad is upset by bending the suspension lead, the thickness of the device can be reduced by the thickness of the upset.
In one embodiment of the present invention, the step (b) further includes a step (b2) of thinning at least a portion of the suspension lead that is close to the die pad.
In one embodiment of the present invention, the thinning is done by a half etching process in the step (b), whereby it is possible to easily produce the structure including the die pad and the lead. Moreover, unlike in the case where a pressing process is employed, no stress is applied to the lead frame during the manufacturing process, whereby it is possible to improve the reliability of the resin-encapsulated semiconductor device to be manufactured. Moreover, when the formation of the lead frame used in the step (a) is done by an etching process, the step (b) can be performed continuously with the step (a), whereby it is possible to reduce the number of steps.
In one embodiment of the present invention, in the step (b), at least a portion of each of the die pad and the lead whose thicknesses are both 200 xcexcm to 300 xcexcm is thinned so that the thicknesses of the die pad and the lead are both 100 xcexcm to 150 xcexcm, whereby it is possible to absorb the stress occurring due to the resin encapsulation while maintaining the strength of the lead frame. Moreover, it is possible to reduce the thickness as compared with a conventional resin-encapsulated semiconductor device.